1. Field of the Invention
The present invention relates to a method for forming a wiring and a method for manufacturing a thin film transistor by dropping a composition into which a material of an object to be formed is mixed. Specifically, the invention relates to a method for forming a wiring and a method for manufacturing a thin film transistor by a droplet discharging method (an ink-jetting method), and further, the droplet discharging method.
2. Description of the Related Art
A droplet discharging method typified by a piezo method or a thermal jet method, or a continuous type droplet discharging method attracts attention. These droplet discharging methods have been used for printing words and drawing images, but they start to be applied to a semiconductor area for forming a minute pattern or the like these days.
A method of forming a film pattern is proposed by Reference 1: the method makes it possible to improve a method of forming a film pattern by an ink-jetting method, make a film thicker, and make a line thinner. Further, problems such as disconnection or short-circuit are not caused in the case of using a conductive film (Reference 1: Japanese Patent Laid Open No. 2003-133691).
According to Reference 1, a substrate is treated in advance so that a contact angle with a droplet is 60 degree, and a droplet is discharged over a whole area for forming a wiring at a larger interval than a diameter of the droplet attached on the substrate, in a first discharging step. A droplet is discharged at a position in the whole area for forming a wiring in a second discharging step, which is different from the position discharged in the first discharging step, at the same interval. In a third discharging step, a droplet is discharged over the whole area for forming a wiring at a smaller interval than the interval in the first discharging step.
Further, plasma exposure in a normal pressure or in vacuum is cited as a surface treatment for controlling a contact angle. Gases used in the plasma treatment can be selected in consideration of a material of a substrate surface on which a conductive wiring is to be formed, and treatment gases such as methane tetrafluoride, perfluorohexane or perfluorodecane can be used, for example, according to Reference 1.